The sarcoplasmic reticulum (SR) membrane from muscle cells is a remarkably smple membrane (approximately 5 major proteins) that carries out a biochemically crucial function (Ca2 ion transport). The major enzymatic activity in this membrane is a Ca2 ion-Mg2 ion dependent ATPase. The ATPase activity and the Ca2 ion transport are correlated. As is the case with virtually every membrane protein, very little is known about the detailed structure of the ATPase. Previous work suggests that four ATPase molecules aggregate to form a Ca2 ion channel. The structure of bacteriorhodopsin leads to the consideration of transmembrane bundles of alpha-helices. In agreement with the suggested aggregation of 4 ATPase molecules, my own studies show that a channel formed from 4 alpha-helices has just the right size for Ca2 ions. We propose to carry out the following preliminary tests of this idea: 1. Using a new SDS-urea-hydroxylapatite chromatography procedure developed in my laboratory for studying hydrophobic peptides, we intend to isolate the membrane-sequestered hydrophobic peptides separated from the remainder of the ATPase by extensive proteolysis. These peptides will be characterized with respect to size, amino acid composition, and N-terminal partial amino acid sequence. Our hypothesis predicts that these fragments should weigh about 3,000 daltons and have hyrophilic ends and hydrophobic centers. 2. Using circular dichroism and laser Raman spectroscopy, we intend to probe the conformation of the membrane-sequestered hydrophobic peptides in situ. Our hypothesis predicts high alpha-helix content for such peptides.